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Double-bosonization and Majid's Conjecture, (IV): Type-Crossings from $A$ to $BCD$

Both in Majid's double-bosonization theory and in Rosso's quantum shuffle theory, the rank-inductive and type-crossing construction for $U_q(\mathfrak g)$'s is still a remaining open question. In this paper, working with Majid's framework, based on our generalized double-bosonization Theorem proved in \cite{HH2}, we further describe explicitly the type-crossing construction of $U_q(\mathfrak g)$'s for $(BCD)_n$ series direct from type $A_{n-1}$ via adding a pair of dual braided groups determined by a pair of $(R, R')$-matrices of type $A$ derived from the respective suitably chosen representations. %which generalize the lower rank cases constructed in \cite{HH1}. Combining with our work in \cite{HH1,HH2,HH3}, this solves Majid's conjecture, that is, any quantum group $U_q(\mathfrak g)$ associated to a simple Lie algebra $\mathfrak g$ can be grown out of $U_q({\mathfrak {sl}}_2)$ inductively by a series of suitably chosen double-bosonization procedures.